Conventional reversed phase silica columns (e.g., ODS) are widely used as general-purpose stationary phases for chromatographic separations (Neue, “HPLC Columns—Theory, Technology, and Practice,” WILEY-VCH, New York, 1997, 183-203). However, some drawbacks, including, for example, “phase collapse” (i.e., dewetting) in highly aqueous environments, weak retention of ionic compounds and residual silanol activity which leads to peak tailing of basic analytes prevent employment of conventional reverse phase silica columns in certain applications.
Polar-embedded phases improve the peak shape of basic analytes and enable operation of reverse phase HPLC columns in highly aqueous environments (O'Gara et al., LC-GC 2001, 19 (6):632-641). Commonly used polar groups include, for example, amides, ureas, ethers and carbamates. In general, polar-embedded phases provide superior peak shapes of basic analytes and are more compatible with highly aqueous environments when compared to general purpose reverse phases. Further, polar embedded phases often have selectivities which are substantially different from those exhibited by conventional C-18 packings.
Surfactants are important components of a variety of consumer, industrial, agricultural and pharmaceutical products. Surfactant analysis is often complicated by the presence of mixtures which are difficult to resolve using conventional chromatography. Surfactants have been analyzed by liquid chromatography on reversed-phase columns (e.g., C18, C8, cyano, phenyl, etc.), normal phase columns, ion-exchange columns and size-exclusion columns (Schmitt, “Analysis of Surfactants,” 2nd edition, Marcel Dekker, Inc, New York, 2001, 197-292). C18 columns provide reasonable separation, peak efficiency and asymmetry, especially for anionic surfactants. However, the presence of underivatized silanols on silica-based reversed-phase columns often prevents satisfactory resolution of cationic surfactants. For example, C18 reversed phase columns fail to separate individual oligomers of polyethylene glycol (PEG) based surfactants. In addition, because of “de-wetting” caused by necessary usage of high aqueous mobile phases, conventional high-density C18 columns are unsuitable for analysis of highly hydrophilic hydrotopes, (e.g., sodium naphthalene sulfonate and xylene sulfonate). Despite the availability of a variety of HPLC columns to analyze a wide range of surfactants using a plurality of different conditions, no single column can be used to separate cationic, nonionic, and anionic surfactants in a single run using simple and volatile, mass spectroscopy compatible, mobile phases.
Accordingly, what is needed are novel silane compounds which have both hydrophobic and polar functionality, substrates functionalized with these new silane compounds and the use of these novel functionalized substrates to simultaneously separate cationic, nonionic and anionic surfactants.